Filter element

ABSTRACT

A filter element adapted to be sealingly clamped in a filter housing. The element comprises a porous hollow cylindrical integral self-supporting bonded fibrous structure. The structure has thermally melt bonded to at least one end thereof, a thermoplastic polymer closed cell foam sealing gasket. The gasket is adapted to provide a sealing surface between the end of the cartridge and the sealing edge of the filter housing. In a preferred embodiment, the sealing edges of the filter housing used in conjunction with the aforedescribed filter element comprises at least two circular sealing edges concentric to the axis of the cylindrical filter element. Such a combination provides a means for determining whether there is leakage past the sealing edges by the discoloration of the sealing gasket area between the concentric sealing edges by the liquid being filtered.

This application is a continuation of Ser. No. 153,875, filed on Feb. 9,1988, now abandoned, which, in turn, is a continuation of Ser. No.038,122, filed Apr. 14, 1987, now U.S. Pat. No. 4,731,184, which, inturn, is a continuation of Ser. No. 736,873, filed May 22, 1985, nowabandoned.

FIELD OF THE INVENTION

This invention relates to filter elements and in particular a means forproviding a novel gasket means for sealing the ends of the filterelement in a filter housing.

PRIOR ART

Filter elements which are porous hollow cylindrical integralself-supporting resin bonded fiber structures are well known in the art.Preferred embodiments of such filters are described in U.S. Pat. Nos.2,539,767 and 2,539,768 to Anderson and sold by the Assignee hereinunder the trademark MICRO-KLEAN (AMF Cuno General Filtration Division,Meriden, Conn.) wherein the bonding system is a thermosetting resin.Another preferred embodiment of the filter element is described in U.S.Pat. Nos. 4,100,009 and 4,197,156 to Nakajma et al wherein the bondingmeans is melt bonding of thermoplastic fiber. Broadly, these filterelements are relatively rigid, self-supporting, thick-walled, tubularmembers composed entirely of a bonded fibrous material. The filterelements are used for filtering liquids and gases by flowing radiallyinwardly under a differential pressure.

Typically the filter elements are designed to obtain maximum filterefficiency by providing a fibrous structure of a graded porosity, withthe size of the pores progressively increasing radially outwardly towardthe outer surface. By virtue of such graduated porosity, or density, asthe fluid flows inwardly through progressively smaller and more numerousinterstices, the particulate contaminant to be filtered out penetratesto varying depths according to their size. Thus, the filter elements canaccomodate more solids without effecting flow, with a consequentlylonger, effective life before the elements need replacing.

For example, in Anderson, the graduated porosity in the filter elementsis accomplished by accreting resin-impregnated fibers from an aqueousuniform dispersion of such fibers under controlled conditions as to theamount of vacuum used in effecting such accretion and as to thecomposition and characteristics of the fibrous stock used.

Typically, these filter elements are adapted to be sealingly clamped ina filter housing. At each end of the cartridge, a sealing edge of thefilter housing engages the end of the cartridge to provide a seal toprevent bypass of the contaminants being filtered from the liquid.Typically, the sealing edge is a circular sealing lip or knife edgeprotruding from the housing which engages the end of the filter elementand is concentric with the axis of the filter. A sealing edge engageseach end of the filter cartridge element. The sealing edge is embeddedinto the end of the fibrous structure to provide a seal between the edgeand filter element. A compression spring means or clamping means is usedto provide sufficient force to embed the sealing edge of the housinginto the end of the filter cartridge element.

The foregoing technique for sealing is adequate for relatively open typeor porous filter elements, i.e. "low efficiency" filter cartridges,since the cartridges are relatively soft, permitting the sealing edge ofthe housing to embed itself into the cartridge end.

In recent years, however, customers have demanded tighter and moreefficient type filter elements. Such high efficiency filter elementsrequire an extremely effective sealing means to prevent the by-pass ofthe filter by the contaminant particles. Typically the high efficiencyfilter elements tend to be very hard. Such structures, by their verynature, make it difficult to achieve the proper embedding of the sealingedge of the filter housing into the cartridge end to provide adequatesealing. For example, a typical cartridge wall is about 3/4 of an inchthick. In order to obtain adequate filtration the fluid should passthrough this complete wall thickness to achieve the desired filtrationresults. If sealing is not adequate the fluid will go over the end ofthe cartridge underneath the sealing edge of the housing and into thefluid outlet thus contaminating the filtered fluid. This can, if thereis enough particulate in the fluid being filtered, cure itself in thatthe particulate will clog this area and provide sufficient filtrationefficiency. However, during start-up this by-pass can result insignificant loss of filtration efficiency.

Attempts have been made to solve this problem, for example, byadhesively bonding an elastomeric flat gasket to the ends of thecartridge. Such gaskets are not completely satisfactory due to the factthat the adhesive may not be solvent resistant to the liquid beingfiltered and the gasket can swell. The adhesives rapidly leach out anddisappear causing contamination of the products and the elastomer gasketswells and disintegrates causing leakage problems. Additionally,elastomeric gaskets can be very expensive. Attempts have been made todesign solid or rigid injection molded plastic end caps which areattached to the ends of these filter elements by means of spin welding,ultrasonic bonding, melt bonding, etc. These end caps, in turn, utilizeelastomeric O-rings and/or flat gaskets which are retained in the endcaps to provide the necessary sealing engagement with the filterhousing. Such a solution to the aforedescribed problem is expensive andadds considerable cost to the filter cartridge element not warranted bythe type fluids being filtered.

Another problem associated with these type of filter cartridge elementsis that it is difficult to quickly and efficiently determine whetherthere is bypass of the contaminant past the housing sealing edge. Thisinvention provides a unique simple and efficient way of determiningwhether there has been leakage past the sealing edges of the filtercartridges.

Various means are known for sealing the ends of filters, none of whichare applicable to the type filters described herein and/or are expensiveand inefficient in use. For example, U.S. Pat. No. 2,726,184 to Cox etal describes a method for improving the end seals of a pleated orconvoluted type filter element. The method includes depositing an amountof unpolymerized, thermosetting adhesive in liquid form on the surfaceof end discs, allowing the deposited adhesive to harden, and then pressfitting the end discs onto the end of the filter element. The adhesivemay be in the form of a precut solid adhesive ring which is placed inthe disc. This method is complicated and expensive and requirespreformed end discs to be sealed to the end of the filter element.

U.S. Pat. No. 2,771,156 to Kasten et al describes a pleated filterelement and resilient plastic end caps, the pleated filter element beingembedded therein. In a process of molding the end cap the ends of thepleated element are immersed in a mold filled with a plastic compositionand cured. When the filter element is removed from the mold the ends ofthe pleats are covered with a tough rubber-like product, i.e. a"plastisol"--a vinyl resin with fillers, pigments, plasticizers and/orstabilizers. Such a "plastisols" tend to have low temperature limits andare incompatible with many solvents.

Additionally, foamed polyethylene and its copolymers are well known inthe art and sold under the trademarks VOLARA and MINICEL by Voltek andknown to be useful as a gasketing material. Such a material, however,has not to Applicants' knowledge, been utilized in sealing filterelements of the type used in this invention.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of this invention to provide a filter element havingimproved means thereon for sealing the ends thereof in a filter housing.

A further object of this invention is to provide a depth type filterelement with a sealing gasket on at least one end which preventscontaminant bypass between the filter housing and filter element.

Still another object of this invention is to provide a filter elementwith a sealing gasket which is compatible with a broad range of fluidsto be filtered.

Yet another object of the present invention is to provide a filterelement having a sealing gasket which is permanently attached to thefilter element without the use of other components which jeopardize thecompatibility of the filter element/gasket combination with the fluidsbeing filtered.

A further object of this invention is to provide a combination filterelement and housing which has a seal means thereon which clearlyindicates whether there is by-pass of the filter.

All of the foregoing objects are accomplished by a filter elementadapted to be sealingly clamped in a filter housing along a sealing edgethereof. The filter element comprises a porous hollow cylindrical,integral self-supporting bonded fibrous structure having thermally meltbonded to at least one end thereof, a thermoplastic polymer closed cellfoam sealing gasket. The gasket provides an effective sealing surfacebetween the end of the cartridge and a sealing edge of the filterhousing.

In a preferred embodiment, the filter element is used in combinationwith a filter housing wherein the sealing edge of the filter housingcomprises at least two circular sealing edges concentric to the axis ofthe cylindrical filter element to provide an indicia area on the gasketbetween the concentric sealing edges which discolors upon exposure tothe fluid being filtered to indicate by-pass of the fluid around thesealing edges. Discoloration of this indicia area will indicate bypassof contaminated fluid past the sealing edges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one end of the filter element of thisinvention.

FIG. 2 is a partial cross-sectional view showing the filter element ofthis invention utilized in a filter housing.

FIG. 3 is a perspective view of one end of the filter element of thisinvention showing a means for securing the sealing edge of the filterhousing thereon.

FIG. 4 is a cross-sectional view of the filter element of this inventionshowing another means for securing the sealing edge of the filterhousing thereon.

FIG. 5 is a cross-sectional view of the filter element of this inventionused in conjunction with concentric sealing edges whereby by-pass offluid around the sealing edges can easily be determined by inspection ofthe sealing gasket.

FIG. 6 is an end view of the filter element of this invention takenalong line 6--6 of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-6, the filter elements used in this invention arewell known in the art. As previously indicated these are produced, forexample, as described in Assignee's U.S. Pat. No. 2,539,767 and2,539,768 to Anderson, the entire disclosures of which are incorporatedherein by reference. The filter elements 10, which this invention is animprovement thereon, have been sold under the trademark Micro-Klean, byAMF Cuno General Filtration Division, Meriden, Conn. Referring to FIG.1, this filter element 10 comprises a relatively rigid self-supportingthick-walled, tubular member composed entirely of resin-impregnated andbonded fibrous material.

Typically such cartridges have deep grooving 11 around the periphery orouter surfaces 12 to increase their dirt holding capacity and to preventpremature blinding of the surface of the filter element by largeparticles.

The element 10 is intended to be used for filtering liquids and gaseswhich are caused to flow radially inward under a differential pressure(see FIG. 2). In order to obtain the maximum filtering efficiency, thefibrous structure of the filter element 10 is of a graded porosity, withthe size of the pores progressively increasing radially outwardly towardthe outer surface 12. By virtue of such graduated porosity, or density,as the fluid flows inwardly through progressively smaller and morenumerous intersticies, the particulate contaminants to be filteredpenetrate to varying depths according to their size.

Such graduated porosity in a filter element is accomplished byaccreting-impregnated fibers from an aqueous uniform dispersion offibers under controlled conditions of vacuum, composition and fibercharacteristics.

The fibrous material employed in making the filter element can be wool,esparto, yucca, cellulose (e.g. wood), glass, acrylic, rayon oradmixtures thereof.

The fibers are mixed with a dispersion of resin particles or resinforming ingredients, either in the form of water or alcohol dispersion.Subsequently, one or more perforate formers or dies are immersed in thesuspension in a felting tank holding the dispersion of solvent, resinand fibers and the resin impregnated fibers are caused to be accretedupon the formers by application of a controlled degree of suctionimposed upon the interior of the formers. By the control of the degreeof vacuum and the length of time over which the vacuum is applied, inconjunction with the proper control of the characteristics of the fiber,a filter carcass is produced of the depth, or thickness and gradedporosity that is desired. The proportion of resin in the fibrous carcassis also a factor when producing a filter element of the desired degreeof strength and hardness to withstand the pressure drop to which it maybe subjected to use.

In order to impart to the filter element strength and rigidity, as wellas to water proof the fibers so that they will not become soggy, or softin the presence of water or other fluids, a resin is used to impregnatethe fibers and to bond them together in a relatively fixed relationship.The amount of resin used may vary between 15% and 60% by total weight ofthe filter element. Various resins including thermosetting resins suchas phenol formaldehyde condensation products, urea formaldehydecondensation products and the melamine resins may be used. Thermoplasticresins may also be employed, such as polystyrene. Preferred resins aremelamine and phenolic resins.

After formation of the wet carcass, a substantial proportion of thewater or other solvent is removed by drawing hot air through the filtercarcass. After drying, the resin is set by blowing air through thefilter carcass under controlled temperature and controlled timecondition. By passing the air through the carcass in one direction toremove the solvent or water and the other direction during the settingof the resin, the uniform distribution of resin throughout the mass ofthe carcass is substantially affected. After setting, the filter carcassis cured by heat under temperature and time conditions appropriate forthe curing of the particular resin used.

In the final step, the filter cartridge is sized to accurate dimensionsby cutting or trimming mechanically as by means of a knife, saw orgrinder. (see the '767 patent to Anderson).

Referring to FIG. 1, the finished filter element 10, comprises a thickwall hollow cylindrical cartridge having concentric outer and innercylindrical surfaces 12 and 14, respectively, and end surface 16 on eachend of the cylinder 10. In use fluid enters from the outside 12 of thecartridge 10, passes through the thick wall of the cartridge and iscollected in the core and then passes to the point of use.

Typically the filter elements are limited to a maximum operatingtemperature of up to 250° F. The filter elements, typically, canwithstand differential pressures up to 160 psid but are operated in the25 to 35 psid range.

Another preferred filter element is exemplified in U.S. Pat. No.4,100,009 to Nakajima, the entire disclosure of which is incorporatedherein by reference. The filter elements are stabilized by hot adhesion.The method of producing such filter elements comprises passing a web ofa gathered fiber layer carried on a conveyor belt through a heatingzone. The web is then heated in such a way that a lower-meltingcomponent of composite fiber contained in the lower part of the webcontacting the conveyor belt is not in the molten state and alower-melting component contained in the upper part of the web is in themolten state. The web is then separated from the conveyor belt, wound ona take-up rod or tube in such a way that the upper surface thereofoccupies the inner side of the winding, while heating the web further,cooling the wound up article and drawing out the take-up rod or tubefrom the shaped product.

The cartridges may be used in varying lengths or multiples of a singlelength, stacked one on top of another. In such arrangements all thecartridges in multiple height stack arrangements are fastened togetherby a cement, e.g. polypropylene, to assure alignment and permanentbonding for positive sealing against bypass.

The filter elements may be used for removing particulate contaminentswhich are fibrous, abrasive or gelatinous from fluids such as gas,alcohol, glycols, coolants, fuels, oils, lubricants, cosmetics, paintsand varnishes, syrups, compressed air, water or sensitive processliquids, e.g. demineralized water, food products, beverages,photographic solutions and, particularly, "dope" for producing magneticrecording tapes.

Referring to FIGS. 1-4, thermally bonded to at least one end 16, andpreferably each end of the filter element 10 thereof is a thermoplasticpolymer closed cell foamed sealing gasket 22. Each gasket 22 provides aneffective sealing surface between the end of the cartridge 16 and thesealing edge 20 of the filter housing 18. Preferably the polymer is apolyolefin, e.g. polyethylene or polypropylene. Such materials arechemically compatible with most of the liquids and gases to be filteredby the elements herein. Due to the characteristics of the polymer, apolyethylene closed cell foam is preferred. Such foams are known in theart, with a preferred brand being sold by Voltek of Lawrence, Mass.under the name VOLARA and MINICEL, with the VOLARA brand beingpreferred. This polymer is a radiation-cross-linked polyethylene foamhaving a fine cell structure and a smooth surface. In particular, thepreferred VOLARA 6A has a thickness of about 1/16th of an inch and hasthe following properties:

(a) Compressive strength at 50% deflection of 25 to 31 psi (by ASTMD-1056)

(b) Tensile strength of 124-148 psi (by ASTM D-1564)

(c) Elongation of 178-220% (by ASTM D-1564)

(d) Tear strength 28-35 lbs/in. (by ASTM D-624).

The gasket is typically in the form of a donut shaped disc circle whichis adhered to the filter end 16 concentric with the central axis 24.Typically the gasket may be of a diameter somewhat smaller than theoutside diameter of the filter element 10, and have an inside diametersomewhat larger than the internal diameter of the filter element.Typically the discs are 1/16 to 3/32 of an inch thick. This dimensioncould be increased if necessary to compensate for troublesome sealingconfigurations that require more resiliency or depth to providesufficient sealing. The foam is obtained in sheet form and cut intodiscs of the desired size and shape.

The gasket 22 is applied to the filter element 10 by heating the end 16of the element 10 to a temperature sufficiently high to thermally meltbond the gasket 22 to the cartridge end 16 when the gasket is contactedto the hard cartridge surface. Such temperature may be determinedreadily and is empirically derived but is below the temperature at whichthe cartridge starts to deteriorate, melt and/or fuse and is also belowa temperature that completely melts the gasket. However, it has beenfound that the cells inside the gasketing material insulate the heatedlower surface in contact with the heated end 16 of the filter 10 fromthe remaining portion of the gasketing material and thus only the lowersurface of the gasket is sufficiently heated to melt bond itself to theend 16 of the filter element 10. Such heating can be accomplished with ahot plate, infrared energy, hot air, etc. There are a number oftechniques available for heating the end of the cartridge which aresimple to accomplish and to automate.

The closed cell configuration of the polymer is also desireable becauseit provides resiliency or spring back that allows compensation for outof alignment or out of flatness of the end of the cartridge.Additionally, the closed cell configuration provides sealing betweencells through which the fluid cannot seep or flow. The use of a solidpolymeric gasket would be inadequate because although it might bond tothe filter element by the mere heating of the end of the cartridge, itwould either completely melt and deform and/or would not providesufficient resiliency for the sealing edges of the filter housing toembed therein.

The filter housings used in conjunction with the filter element of thisinvention are well known in the art. Portions of such a housing aredepicted in FIGS. 2-4.

As shown in FIG. 2, the filter element 10 is intended to be clampedendwise between the heads of the filter housing, generally 18. Sincefiltration through the element 10 is affected by maintaining asubstantial pressure differential between the outside 12 and inside 14of the filter 10, it is essential that the filter element 10 have asufficient degree of compressive strength and/or hardness to withstanddeformation under the loads to be applied thereto.

Still referring to FIG. 2 and additionally FIG. 3, a plurality of filterelements 10 are disposed in the filter housing as indicated, with thesealing edges 20 of the filter housing which are typically circularknife edges concentric to the axis 24 of the filter element 10,embedding into the gasket 22 on filter element 10. FIGS. 2, 3 and 4depict well known means for securing and sealing the filter element 10in the filter housing and sealingly engaging the sealing edge 20 againstthe end 16 of the filter element 10 which has thereon gasket 22.

FIG. 2 shows one type of housing 18 wherein the sealing edges 20 of thehousing 18 embed themselves in the gasket 22 to provide sufficientsealing to prevent by-pass of the fluid from outside of the filterelement into the center of the filter element. In FIG. 3, is a preferredembodiment the sealing edges 20 of the filter housing are springcompressed by spring 26 against the gasket 22 to form an appropriateseal, the gasket 22 being effective to provide adequate sealing betweenthe sealing edges 20 and the end 16 of the filter element.

FIG. 4, depicts another embodiment wherein the sealing edges 20 aremolded onto a knob 28 which is threaded unto a rod 30 going through thecenter of the filter 10 sealingly to compress the edges 20 into gasket22. A similar type arrangement is on the other side of the filterelement. This arrangement is then inserted in a filter housing.

FIGS. 5 and 6 depict another type sealing edge consisting of at leasttwo concentric sealing edges 20 A and 20 B which when urged against thegasket 22, produces therebetween an indicia area 32 on gasket 22. Afteruse, or after an initial test period, the adequacy of the seal isdetermined by mere inspection of the area 32. If there is leakagethrough the sealing edges 20 A and 20 B, the area between these edgeswill be discolored. For example if the filtering liquid or the particlescontained in a liquid are of a darker color than the gasketing material,the indicia area 32 between the gasketing rings will be somewhat darkerif there is leakage, but will maintain substantially the same color asthe original gasket if there is no leakage.

What is claimed is:
 1. A filter element comprising:a tubular filterstructure having at least one end adapted to coact with a housing forthe filter; annular gasket means for sealing the end of the filter witha coacting housing for the filter; the gasket means comprising: apreformed sheet of resilient thermoplastic closed cell foam; the surfaceof the gasket sheet remote from said filtering structure, being adaptedto resiliently coact with a filter housing; the surface of the gasketsheet abutting said filtering structure having a melt surface, the meltsurface being integral with and formed from the gasket sheeting; andadhering means to adhere the gasket to the end of the filter consistingof the surface of the melted closed cell material of the gasket.
 2. Thefilter element of claim 1, wherein the polymer is a polyolefin.
 3. Thefilter element of claim 1, wherein the polymer is a polyethylene.
 4. Thefilter element of claim 1, wherein the polymer is a radiationcross-linked polyethylene.
 5. The combination filter element and housingtherefor comprising:the filter element of claim 1, 2, 3 or 4, and afilter housing having a sealing edge for engaging the surface of thegasket sheet remote from the filtering structure to sealingly andresiliently coact therewith.
 6. The combination of claim 5, wherein thesealing edge comprises at least one circular removable sealing edgeconcentric to the axis of the tubular filter structure.
 7. Thecombination of claim 6, wherein there are at least two concentriccircular removable sealing edges to provide an indicia area on thegasket between the concentric sealing edges which discolors uponexposure to the filtration fluid to indicate bypass of the fluid aroundthe sealing edges and when said sealing edges are removed the indiciaarea may be observed.